A popular type of multimedia projection system employs a broad-spectrum light source and optical path components upstream and downstream of an image-forming device, such as a liquid crystal display (“LCD”) or a digital micro-mirror device (“DMD”), to project the image onto a display screen. An example of an LCD projector that includes a transmissive LCD, a light source, and projection optics to form and project display images is manufactured and sold under the trademark LP® and LitePro® by InFocus Corporation of 27700B SW Parkway Avenue, Wilsonville, Oreg. 97070-9215, the assignee of the present application. An example of a DMD-based multimedia projector is the InFocus LP420 model.
A typical broad-spectrum light source used in a multimedia projector is a high-intensity discharge (HID) lamp. The light from the HID lamp is collected in a reflector that shapes the light and pushes it forward into the projection optics. However, the HID lamp generates such an intense amount of light and radiation that a reflector alone cannot address all of the safety and operational concerns associated with using an HID lamp in a multimedia projector. For example, the HID lamp is prone to explosion under certain conditions. Moreover, during operation light and radiation may get into areas of the projector where it can be harmful, damaging sensitive electronic and optical components or melting the surrounding plastic components. As is often the case, stray visible light may escape from the projector altogether and reduce the visibility of the projected image. The radiation and resulting heat generated by the light source also presents a secondary problem of noise generated by the fans used to cool the lamp, lamp reflector, and surrounding parts of the projector.
Several different types of reflectors have been designed in an effort to overcome some of these safety and operational concerns. For example, cold mirror glass reflectors reflect most of the visible light forward, but allow the ultraviolet (UV) and infrared (IR) radiation to pass through. But glass reflectors may not adequately contain an HID lamp explosion. Moreover, the UV and IR radiation passing through the reflector can be particularly harmful when striking other parts of the projector causing them to overheat, sometimes to the point of melting. Heat sinks have been used to conduct heat from the walls of the reflector to the exterior of the projector or to the circulating air within, but prior art heat sinks are typically unsuited for use in a multimedia projection system as they may be too large or too heavy or otherwise interfere with the operation of the projector.
An alternative reflector is an aluminum reflector which reflects the visible light and all of the IR radiation into the optical chamber. While an aluminum reflector may contain the HID lamp in the case of an explosion and may reduce the amount of heat radiated to some parts of the projector, it presents other problems since the IR radiation adversely affects the sensitive optical components present in the optical chamber.